The scattered radiation patterns of surface cracks irradiated by acoustic surface waves are interpreted to provide estimates of crack size. The technique is demonstrated for cracks as small as 100 &mgr;m in radius with an accuracy of about 10%.The key features are the positions and spacings of nulls in the angular dependence of the backward scattered surface‐wave intensity. A simple model based on optical diffraction theory is presented and demonstrated on cracks (made with the identation technique) in commercial hot‐pressed silicon nitride studied at 100 MHz and on cracklike flaws in commercial aluminum studied at 2–10 MHz.